Control systems, which include process control systems and safety instrumented systems (SIS), typically implement one or more controllers to control the process or safety system. The controllers in these systems frequently use field devices to perform a variety of functions within the control environment. For example, in a level control system, the field devices may be used to monitor and/or control the amount of a liquid in a holding tank. When the level of the liquid has reached a predetermined position (high or low), the control system may respond by utilizing one of the field devices, such as a valve, to adjust the flow of liquid entering or exiting the holding tank.
In many control systems, there may be a component of a field device that is required to move during normal operation. The implementation and/or operating environment of the field device may subject the movable component of the field device to high loads, such as high pressure or friction loads, which may contribute to the movable component's inertia at rest. For example, the movable component may be a valve or lever that is idle for a substantial period of time during normal use. A motor is commonly used by the control system to actuate such a movable component. To move the movable component, the motor must overcome the movable component's inertia at rest. In overcoming the movable component's inertia at rest, the motor may draw electrical current from its power source at levels beyond the prescribed operating range of the motor. Although it may be possible to utilize larger motors that are capable of safely operating at higher amounts of electrical current, the larger motors are more expensive and may not be readily adaptable for configuration within an existing control system.